The present invention relates to method and apparatus for distributing and processing information, and more specifically relates to method and apparatus for preventing unauthorized use of information by partially encrypting such information.
With the advance of electronic and communication technology, information conveyed in electronic form (xe2x80x9celectronic contentxe2x80x9d) is fast becoming the most economic and reliable way of distributing information. However, many information providers are reluctant to distribute electronic content because it is very easy to copy and use the information without authorization. In spite of the existence of copyright law, experience shows that electronic content are often copied and used without paying any royalties to copyright holders. Thus, in order to promote the use of electronic conveyance of information, means must be develop to prevent unauthorized usage and copying of electronic content.
Methods have been developed to prevent unauthorized copying of electronic content. Several years ago, these methods were used by many software developers. However, these copy protection methods do not find acceptance in the market place. Consequently, the majority of computer software is currently marketed without copy protection.
Recently, attention has been turned towards preventing unauthorized uses. For example, several companies market xe2x80x9cdongles,xe2x80x9d or hardware keys, which are attached to a port of a computer. Protected software would not execute in a computer without an appropriate key. Thus, the protected software could be copied but cannot be used in an unauthorized computer. However, many users found that these software and hardware keys cause much inconvenience. For example, when a user wishes to remove the software from one computer and execute the software in another computer, the associated hardware key has to be moved. So far, no mass marketed software uses hardware key to protect against unauthorized uses.
Other methods have been developed to prevent unauthorized usage of electronic content. One of the methods is disclosed in U.S. Pat. No. 5,010,571 issued to Katznelson. It discloses a system for controlling and accounting for retrieval of data from an optical storage medium containing encrypted data files from which retrieval must be authorized. The optical storage medium is distributed to customers at nominal or no charge. However, in order to decrypt the data files, a customer must obtain a decryption key from a remote authorization and key distribution station. As a result, unauthorized uses can be prevented. A similar system is disclosed in U.S. Pat. No. 4,827,508 issued to Shear. In Shear, the decryption key is stored in a secure device in the customer site. The secure device also stores accounting data relating to usage of the electronic content. The accounting data is periodically sent to a billing station.
In the above methods disclosed by Katznelson and Shear, vast amount of distributed information is encrypted using a single key (or a small number of keys). Thus, if the decryption key is inadvertently made public, all these information can be used without paying the information providers. Naturally, information providers are reluctant to rely on these methods to distribute their valuable asset (i.e., information).
Another problem with these prior art methods is that information providers cannot match the security level of encryption to the value of the information. Typically, the security of encryption is directly related to the complexity of encryption algorithm and the length of keys. The choice of encryption algorithms and the length of keys require an analysis of the value of the information and the costs of encryption. In the methods disclosed by Katznelson and Shear, all information is encrypted using the same key. Thus, this key may not match the requirements of many information providers.
A further problem of these prior art method is that the encryption algorithm is fixed at the time encrypted information is initially distributed. As the installed base of encrypted information increases, it becomes difficult to change the encryption algorithm. Thus, these methods cannot use new cryptographic methods, which may be developed in future.
Another method is disclosed in U.S. Pat. No. 5,247,575 issued to Sprague et al. It discloses that encrypted information may be electronically transmitted from a remote site to a receiving device in a customer site via wired or wireless means. It also discloses that the decryption key could be stored in a removable xe2x80x9ckeyxe2x80x9d card. The card can be inserted into the receiving device to decrypt the received and encrypted data. This method suffers the same defects described above in connection with Katznelson and Shear. In addition, this method requires a communication channel having a large bandwidth for transmitting the encrypted information.
Broadly stated, the invention involves a method and system for distributing and processing digital information. The digital information is separated into two portions. The first portion is a clear portion and the second (residual) portion is encrypted. The clear and the encrypted portions are sent to a processing system that decrypts the encrypted portion. The clear and decrypted portion is combined to obtain a result that is substantially the same as the original digital information.
In one embodiment of the present invention, the clear portion is distributed to customers at no or nominal cost. The residual portion will be stored in a central station. When a customer wishes to use the digital information, the central station encrypts the residual portion using an encryption-decryption key-pair generated at that time. The encrypted portion and the decryption key are sent to the processing system in a secure manner. As a result, different keys can be used to encrypt and decrypt the same information at different times.
One feature of the present invention is that the clear portion is selected in a way to render the reconstruction of the original digital information difficult if the residual portion is not known. Thus, a customer will not be able to reconstruct the original digital information based on the clear portion. As a result, unauthorized use of the digital information is prevented.
In the present invention, the information providers control the choice of encryption algorithms and keys. Further, algorithms and keys can be changed at will.
These and other features and advantages of the present invention will be fully understood by referring to the following detailed description in conjunction with the accompanying drawings.